In the manufacture of a semiconductor device or the like, a fine pattern is formed by photolithography and, in a fine pattern transfer process where the photolithography is performed, a transfer mask is used. In general, the transfer mask is obtained by forming a desired fine transfer pattern in a light-shielding film of a mask blank as an intermediate product in which the light-shielding film is formed on a glass substrate. Therefore, the properties of the light-shielding film of the mask blank as the intermediate product almost exactly determine the performance of the obtained transfer mask. Conventionally, a material composed mainly of chromium (Cr) has been widely used as a material of the light-shielding film. Following the miniaturization of transfer patterns, the wavelength of exposure light for use has been shortened to KrF excimer laser light (wavelength: about 248 nm) and further to ArF excimer laser light (wavelength: about 193 nm), but it is becoming difficult to further shorten the exposure light wavelength in the transmission photolithography. Nevertheless, the miniaturization of transfer patterns has advanced to DRAM hp45 nm and further to DRAM hp32 nm so that the pattern pitch (about 190 nm in hp45 nm generation) of transfer masks has become shorter than the wavelength of ArF exposure light, thus resulting in a strict requirement for the accuracy of the transfer patterns.
With higher integration of semiconductor devices, fine patterns exceeding the transfer limit of the conventional photolithography have been required. In view of this, the extreme ultraviolet (EUV) lithography using EUV light with a shorter wavelength is expected to be promising. Since the EUV light has an extremely short wavelength of about 0.2 to 100 nm, a reflective mask disclosed in JP-A-2002-246299 (Patent Document 1), for example, is used as a transfer mask for transferring a fine pattern. This reflective mask has a multilayer reflective film formed on a substrate and adapted to reflect EUV exposure light and a buffer layer of silicon oxide formed on the multilayer reflective film and further has an absorbent film formed in a pattern on the buffer layer and adapted to absorb the exposure light. The absorbent film is made of materials composed mainly of tantalum. Specifically, in order to suppress the reflectance for inspection light with a wavelength of 150 nm to 300 nm, the absorbent film has a two-layer structure comprising a lower layer of Ta or TaN and a surface layer of TaO.
On the other hand, as described in JP-A-2008-268980 (Patent Document 2), a reduction in thickness of a resist is becoming important for forming a pattern in a light-shielding film by dry etching in a mask blank for ArF exposure. In the case of a conventional light-shielding film made of a material composed mainly of chromium, a chlorine-based gas containing oxygen is used as an etching gas in dry etching for forming a transfer pattern in the light-shielding film using a resist pattern as a mask. However, the resist is poor in resistance to oxygen plasma and thus is significantly reduced in amount during dry etching of the light-shielding film and, therefore, the reduction in thickness of the resist is not easily achieved. In view of this, in order to achieve the reduction in thickness of the resist, Patent Document 2 proposes a method of manufacturing a mask by processing a mask blank in which an antireflection layer in the form of a metal compound film that is not substantially etchable by oxygen-free chlorine-based (Cl-based) dry etching but is etchable by at least one of oxygen-containing chlorine-based ((Cl+O)-based) dry etching and fluorine-based (F-based) dry etching is laminated on a light-shielding layer in the form of a metal film that is not substantially etchable by oxygen-containing chlorine-based ((Cl+O)-based) dry etching but is etchable by oxygen-free chlorine-based (Cl-based) dry etching and by fluorine-based (F-based) dry etching. This method comprises a first step of patterning the antireflection layer by F-based dry etching using a resist mask (resist pattern) pattern-formed on a main surface of the antireflection layer and a second step of patterning the light-shielding layer by Cl-based dry etching using the patterned antireflection layer as a hard mask. In Patent Document 2, tantalum (Ta) is cited as a metal applicable to the metal film forming the light-shielding layer.
JP-A-2001-174973 (Patent Document 3) discloses a halftone phase shift mask comprising a halftone phase shift film containing a tantalum silicide-based material. Specifically, the halftone phase shift film has a two-layer structure comprising a first layer formed of metal tantalum and a second layer formed of an oxide of tantalum silicide. The second layer is formed by DC magnetron sputtering using a mixed target of tantalum and silicon and using a sputtering gas containing oxygen. When forming a transfer pattern in the halftone phase shift film, the first and second layers are continuously dry-etched using a CF4 gas as an etching gas.